1. Field of the Invention:
This invention relates to a film tubing device for use in a packaging apparatus, and more particularly to improvements in such a film tubing device that is capable of forming a continuous length of a film into a tubular shape for enclosing a plurality of successively supplied articles to be packaged.
In the following description, the term "tube (or tubular)" is used to refer to an elongate hollow body or column which may be optional (circular, oval, rectangular, etc.) in cross section. The term "tube" is also used as a verb to form a film or sheet into a tubular shape.
2. Description of the Prior Art:
In packaging each of successively supplied articles by an enclosure made of a heat-meltable, heat-shrinkable film, it is a common practice to first form a continuous length of such film into a tube surrounding the article with both longitudinal side edges of the film heat-sealed together. Then, the film tube thus formed is transversely heat-sealed and cut at two positions slightly ahead of and behind the article to provide a film container completely enclosing the article. Finally, the film container is subjected to hot air treatment, whereby the film container comes into intimate contact with the article inside.
A film tubing device usable for such packaging operation is disclosed for example in Japanese Utility Model Laid-open No. 51-10170 (Laid-open: Jan. 24, 1976; Application No. 49-82215; Filed: July 10, 1974; Applicant: Ibaragi Seiki Kabushiki Kaisha; Inventor: Sen SUGA). For convenience of explanation, the arrangement of the film tubing device disclosed in this laid-open application is illustrated in FIG. 4 of the accompanying drawings and described hereinbelow.
Referring to FIG. 4, the prior art film tubing device comprises a tube former 100 which includes an inner former member 101 in the form of a channel member and an outer former member 102 in the form of a rectangular tube having a longitudinal bottom outlet 103. A continuous length of a film 104, which is originally flat when paid out from an unillustrated roll, is transferred through the former 100 and thereby formed into a tubular shape with both longitudinal side edges 104a overlapping each other and projecting downward through the outlet 103. A pair of heat rollers 105 (longitudinal sealer) which are rotated by a drive mechanism (not shown) are disposed immediately below the former 100 to nip and heat-seal the overlapping side edges 104a of the film 104. Each of the heat rollers 105 has a circumferential groove 106. A cutter knife 107 is arranged in front of the rollers 105 and has its cutting edge in pressing contact with the circumferential groove 106 of one of the rollers 105, so that residual lower portions of the overlapping side edges 104a are cut away.
It is to be noted that the inner former member 101, which is illustrated in FIG. 4, is in fact not illustrated in the drawings of the laid-open application. However, such inner former member must be provided within the film tube 104 since otherwise the film 104 cannot hold its tubular shape. Further, an article to be packaged must also be present within the inner former member 101 though not illustrated in FIG. 4 nor in the drawings of the laid-open application.
The above described prior art film tubing device has a drawback that the film 104 may unexpectedly melt or shrink upon stoppage in transfer of the film 104 when, for example, a new article to be packaged does not come into the former 100 for some reason. More specifically, the outer former member 102 is always at an elevated temperature by being exposed to the heat of the rollers 106, so that upon stoppage in transfer of the film 104 a particular portion thereof is kept in contact with the heated outer former member 102 for a time period enough to melt or shrink the film 104. Such unexpected melting or shrinkage of the film 104 not only causes a waste thereof but also poses a trouble in re-starting a normal film tubing operation.
One way to overcome the above problem is to move the heat rollers 105 to locations laterally outwardly of the former 100 upon stoppage in transfer of the film 104. However, a mechanism required for moving the rollers 105 in this way becomes inevitably complicated and thus costly because the rollers 105 are already connected to their own rotary drive mechanism as described hereinbefore.
Another way conceivable to eliminate the above problem of the prior art film tubing device is to interpose an insulator panel between the outer former member 102 and each roller 105. Naturally, such an insulator panel must have a sufficient thickness to ensure intended heat insulation, so that the spacing between the outer former member 102 and each roller 105 must be correspondingly large for interposition of the insulator panel. Thus, this countermeasure gives rise to a new disadvantage that the length of the overlapping side edges 104a of the film 104 becomes unacceptably large, which results in poor packaging.
A film tubing device which is similar in arrangement and problem is also disclosed in Japanese Utility Model Laid-open No. 57-67903 (Laid-open: April 23, 1982; Application No. 55-143494; Filed: Oct. 7, 1980; Applicant: Ibaragi Seiki Kabushiki Kaisha; Inventor: Sen SUGA).